Friday, 5 January 2018

New research to investigate human impact on the Yangtze River...by Linghan Zeng

One of our collaborators from China (at the
back) and me collecting sediment core

Hello, I am Linghan, a PhD student within the School of Geography at University of Nottingham which is a part of the Centre for Environmental Geochemistry at BGS. I have recently started by PhD on using lake sediments to investigate how lakes in the middle Yangtze floodplain respond to multiple stressors created by human impact.

The Yangtze River which has a length of ca. 6400 km is the third longest river in the world. The various societal, economic and biological benefits that the Yangtze floodplain provided make it appealing and productive for human to inhabit. In 2011, more than 300 million live in the middle and lower Yangtze floodplain and it generates more than 20% of the nation’s agricultural production. Over the last several decades, large amounts of pollutants have been generated with the rapid expansion in population and agricultural and industrial activities. As a result, lakes in this area are severely polluted and some of them are faced with the problem of algae bloom. In addition, more than 50 thousand dams (e.g. the Three Gorges Dam) have been established in this flooding area for benefits such as flood control and hydropower, which may influence the floodplain lakes by changing the hydrological condition. The plan is to use palaeolimnological proxies (including chlorophyll and carotenoid pigments, chironomids, C/N ratios and stable carbon and nitrogen isotopes) to examine the combined effects of hydrological modification and increasing pollutants on the ecohydrological evolution of lakes in the middle Yangtze floodplain.

The plan is to combine the geochemical data with historical archives which will help to quantify the relationships among eutrophication, aquatic plant coverage, hydrological connectivity and organic matter cycling. As well as improving our understanding of floodplain lake ecology and ecosystem dynamics, we will be able to provide a regional overview of the consequences of these changes for shallow freshwater lakes in the middle reaches of the Yangtze floodplain.

Fuchi dam constructed at the confluence of the Yangtze River and Honghu Lake in 1971

In the first instance this study is based on sediment cores from six shallow freshwater lakes spanning the middle section of the Yangtze River. Two of them are freely connected with the Yangtze River and the others have experienced hydrological modification caused by the dam construction. Sediment cores from the six lakes have been collected and dated, and in June samples from surface sediments, catchment soils, seston, submerged and emergent aquatic macrophytes were collected to facilitate interpretation of downcore changes.

At the moment the analysis of the carbon and nitrogen isotopes is underway at the BGS and it is hoped that these will help to track the source of organic matter in ecosystem state change and provide information about the productivity of these shallow freshwater ecosystems.